This Program Project addresses among the most important questions in stem cell medicine and biology through responsible studies on the potentials of pluripotent stem cells from humans (hESC) and nonhuman primates (nhpESC) during development in vitro and in utero, and after transplantation in vivo. Conceptually, the overarching themes are the molecular foundations of ESC and Embryonic Germ (EG) cell properties of Pluripotency, Genomic Imprinting, and Differentiation, under the directions of Gerald Schatten, Ph.D. (Project I Project Leader, PL), Roger Pedersen, Ph.D. (Project II PL) and Peter Donovan, Ph.D. (Project III PL). Each of the three research projects, along with three technological cores and an administrative one, address interrelated fundamental and pre-clinical problems. Project I, Imaging nhpES Cells in Vitro, in Chimerae, and after Transplantation (G. Schatten, PL) investigates the developmental potentials of nhpESC and nhpES derived after nuclear transfer (NTnhpES) by examining chimerae and genomic imprinting. Project II, Differentiation and Epigenesis of Pluripotent Stem Cells (R. Pedersen, PL) examines the earliest post implantation embryos, pluripotent cells and their progeny for imprint normalcy, and to determine differentiation stability. Project III, Derivation and Safety Testing of Non-human Primate Embryonic Germ Cell Lines (P. Donovan, PL) investigates primordial germ cells in vivo, derives nhpEG and compares their developmental potentials with ESCs, while analyzing genomic imprinting in utero and in vitro during reproduction. Imaging Core A (Eric Ahrens, Core Leader, CL) non-invasively images in utero development, ESC/EGs in vitro, and tracks transplanted nhp/hESCs with specific probes in vivo. Primate Core B (Laura C. Hewitson, CL) provides NHP embryos, maintains pregnancies, evaluates, and performs transplants. The Administrative Core C fosters communication, dissemination, and coordination within this Program Project and throughout NIH's stem cell research communities by research planning, real-time data transfer, conferences, and scientific exchanges, as well as our advanced laboratory course Frontiers in Human Embryonic Stem Cell Research. Stem Cell Core D maintains, preserves, and quality controls new and existing nhpES/EG cell lines, distributing them to the projects and freely to other academic investigators. Complementing NIH's new Stem Cell Centers, our multidisciplinary team will make major contributions towards swiftly and accurately addressing key questions whose answers are the essential foundation for stem cell clinical studies.